This invention relates to electrodynamic transducers. It is disclosed in the context of a moving coil loudspeaker, but is believed to have utility in other applications as well.
A number of different loudspeaker constructions involving a number of different types of suspensions are known. There are, for example, the loudspeakers illustrated and described in the following U.S. Pat. Nos. 2,201,059; 2,295,483; 3,930,129; 4,146,756; 5,715,324; and, 5,729,616. This listing is not intended as a representation that a thorough search of the prior art has been conducted or that no more pertinent art than that listed above exists, and no such representation should be inferred.
A loudspeaker has a fairly limited range of approximately linear motion of its voice coil, diaphragm and other moving parts including the suspension components for the voice coil and diaphragm. Nonlinearity increases gradually as the diaphragm excursion increases up to a limit set by the geometry of the motor structure and/or the physical limitations set by the suspension components. The linearity, or nonlinearity, is often illustrated by a plot of force versus displacement. From the force versus displacement function or curve, the maxima of substantially linear movement can be ascertained. This is what is generally referred to as the xe2x80x9cflatxe2x80x9d region of the force versus displacement curve. When the loudspeaker is driven beyond this region, it does not transduce the input current to sound faithfully. This inaccuracy is frequently referred to as harmonic distortion. In the past, to reduce harmonic distortion, the roll height, the depth of the convolutions of the suspension spider and cone surround, was increased. However, increasing the roll height can lead to xe2x80x9coil canning,xe2x80x9d the inversion of one or more rolls, which causes a discernible xe2x80x9cpopxe2x80x9d when the inverted roll(s) revert(s) to substantially its (their) designed orientation(s). Increasing the roll height also reduces the lateral stability of the moving mechanism of the loudspeaker, which may result, for example, in side-to-side movement of the voice coil in the air gap with its attendant consequences.
According to one aspect of the invention, an electrodynamic transducer includes a frame, a magnet assembly providing a magnetic field across an air gap, a voice coil, a coil former for supporting the voice coil in the air gap, a diaphragm having an outer perimeter and an apex, and a surround coupled to the outer perimeter and the frame to support the outer perimeter from the frame. The coil former is coupled to the apex so that current through the voice coil causing the voice coil to move in the air gap causes the diaphragm to move. The surround has convolutions radially outward from the outer perimeter. The convolutions include truncated arcs.
Illustratively according to this aspect of the invention, the convolutions also include generally straight sections extending between adjacent truncated arcs.
Further illustratively according to this aspect of the invention, the depth of the truncations is non-uniform with increasing distance from the outer perimeter.
Additionally illustratively according to this aspect of the invention, the depth of the truncations increases with increasing distance from the outer perimeter.
Alternatively illustratively according to this aspect of the invention, the depth of the truncations varies quasi-randomly with increasing distance from the outer perimeter.
According to another aspect of the invention, an electrodynamic transducer includes a magnet assembly providing a magnetic field across an air gap, a voice coil, a coil former for supporting the voice coil in the air gap, a diaphragm having an apex, and a spider coupled to the coil former to support the voice coil in the air gap. The coil former is coupled to the apex so that current through the voice coil causing the voice coil to move in the air gap causes the diaphragm to move. The spider has convolutions radially outward from the coil former. The convolutions include truncated arcs.
Illustratively according to this aspect of the invention, the convolutions also include generally straight sections extending between adjacent truncated arcs.
Further illustratively according to this aspect of the invention, the depth of the truncations is non-uniform with increasing distance from the coil former.
Additionally illustratively according to this aspect of the invention, the depth of the truncations increases with increasing distance from the coil former.
Alternatively illustratively according to this aspect of the invention, the depth of the truncations varies quasi-randomly with increasing distance from the coil former.